今天遇到了,讀取Arc<Option<String> 類(lèi)型變量值的問(wèn)題,大概意思是這樣的:
use std::sync::Arc;
fn main() {
let foo: Arc<Option<String>> = Arc::new(Some("hello".to_string()));
if foo.is_some() {
println!("{}", foo.unwrap());
}
match foo {
Some(hello) => {
println!("{}", hello);
}
None => {}
}
}
一編譯就報(bào)錯(cuò)了
error[E0308]: mismatched types
--> src/main.rs:11:9
|
11 | Some(hello) => {
| ^^^^^^^^^^^ expected struct `std::sync::Arc`, found enum `std::option::Option`
|
= note: expected type `std::sync::Arc<std::option::Option<std::string::String>>`
found type `std::option::Option<_>`
error[E0308]: mismatched types
--> src/main.rs:14:9
|
14 | None => {}
| ^^^^ expected struct `std::sync::Arc`, found enum `std::option::Option`
|
= note: expected type `std::sync::Arc<std::option::Option<std::string::String>>`
found type `std::option::Option<_>`
在網(wǎng)上查了查,果然有好辦法:
match *foo {
Some(ref hello) => {
println!("{}", hello);
}
None => {}
}
// 或者:
match Option::as_ref(&foo) {
Some(hello) => {
println!("{}", hello);
}
None => {}
}
// 或者:
if let Some(ref hello) = *foo {
println!("{}", hello);
}
// 或者:
if foo.is_some() {
let f1: &Option<String> = foo.as_ref();
let f2: Option<&String> = f1.as_ref();
let f3: &String = f2.unwrap();
println!("{}", f3);
println!("{}", foo.as_ref().as_ref().unwrap())
}
